Selinexor treatment of murine fetal liver cells inhibits mature MK formation. Murine fetal liver cells were treated with selinexor at indicated doses on D1 of maturation, and the MK population was quantified with FACS (A) and visualized under the microscope on D4 (B). ****P < .0001 vs DMSO control. Bars represent 50 μm; n = 4. (C-E) Murine fetal liver cells were dosed with selinexor at D1, D2, or D3 of maturation either continuously until D4 (red bars) or selinexor was washed out after 6 hours (blue bars). On D4, the MK population was quantified with FACS. Values were normalized to DMSO control for each biological replicate, and then replicates averaged. *P < .05; **P < .01; ***P < .001; ****P < .0001 vs DMSO control; n = 3. (F) Human CD34⁺ peripheral blood cells were continuously treated with selinexor beginning on D3 of maturation at the indicated doses, and the number of mature MKs was quantified by FACS based on CD41/61 positivity on D6, D10, and D14. *P < .05; n = 4.